Actuating unit for a heat exchanger, heat exchanger, and a method for controlling a heat exchanger

ABSTRACT

A control unit for a heat exchanger is programmed to receive information on an ambient temperature, an ambient humidity, an amount of water of a wetting device for wetting the heat exchanger and a number of rotations of a ventilator of the heat exchanger and to calculate an amount of spray water based on the information and set the wetting device to wet the heat exchanger with the calculated amount of spray water.

CROSS-REFERENCE APPLICATION

This application is a U.S. National Stage Application of International Application No. PCT/EP2014/072287, filed Oct. 17, 2014, which claims priority to European Application No. 13189793.6, filed Oct. 22, 2013, the contents of each of which is hereby incorporated herein by reference.

BACKGROUND

1. Field of Invention

The invention relates to an control unit for a heat exchanger and to a method of regulating a heat exchanger.

2. Background Information

Today, products, processes or media have to be cooled or frozen in the most diverse sectors of industry. For this purpose industrial cooling plants are used which are generally configured for large cooling performances and for this reason have a large demand in energy which cannot be disregarded.

In order to reduce this demand in energy, different solutions are already known. On the one hand, a manner of construction of the heat exchanger can be changed, for example, a wetting device can be provided, on the other hand, the operating state of individual heat exchanger devices, for example, of a ventilator or of the wetting device can be regulated or controlled. For example, a wetting of the heat exchanger is disclosed in WO 2010/040635 A1. The wetting of the heat exchanger in this respect has the effect that the demand in energy of the ventilators can be minimized or that the degree of efficiency of the heat exchanger can be increased.

Having regard to these so-called hybrid coolers and/or hybrid dry coolers such as they are also disclosed e.g. in WO90/15299 or EP 428 647 B1 the gaseous or liquid medium to be cooled flows through the primary coolant circuit of a heat exchanger and provides the heat to be discharged via a transfer element and/or a plurality of heat exchanger fins partly as sensible heat and partly as latent heat to an exchange fluid. In this respect, one or more ventilators convey the exchange fluid as an air flow through the heat exchanger and can have a variable number of rotations. The discharge of latent heat takes place by means of a wetting fluid as a liquid film forming drops at the air side to the heat exchanger. The excess wetting fluid drops directly beneath the heat exchanger back into a collection vessel.

SUMMARY

In this connection it is a disadvantage that an amount of spray water of the wetting fluid does not correspond to an amount of evaporation so that an excess of water arises which has to be collected in the collection vessel. A further disadvantage in this connection is that a formation of contaminations, for example bacteria, this means legionella has to be avoided. Likewise the number of rotations of the ventilator is not matched to the amount of spray water so that the heat exchanger as a whole is operated in an uneconomic manner and not efficient in energy.

For this reason it is an object of the invention to make available an control unit, a heat exchanger and a method of regulating a heat exchanger for a more economic and/or more energy-efficient mode of operation of the heat exchanger.

This object is satisfied by an control unit for a heat exchanger having the features disclosed herein, by a heat exchanger having the features disclosed herein and by a method of regulating a heat exchanger having the features disclosed herein.

In accordance with the invention, a control unit for a heat exchanger is suggested. The control unit receives information on an ambient temperature, an ambient humidity, an amount of water of a wetting device for wetting the heat exchanger, a number of rotations of a ventilator of the heat exchanger and/or a geodetic level. The control unit is provided for the purpose of calculating an amount of spray water in dependence on the said information and the control unit sets the wetting device in such a way that the wetting device wets the heat exchanger with the calculated amount of spray water.

The heat exchanger comprises a module that can, for example, comprise a plurality of transfer elements having a plurality of heat exchanger fins. The transfer elements can be configured as tubes or as an extruded section having a plurality of passages. The heat exchanger fins can, for example, be fins or edged sheet metal strips in finned shape. The heat exchanger fins can be connected to the transfer elements in a heat conducting manner and can form an air passage. Moreover, the heat exchanger can comprise a ventilator, wherein the ventilator can produce an air flow in the air passage. Moreover, a wetting device for the heat exchanger can be provided, wherein the wetting device is arranged at the heat exchanger and wets the heat exchanger with a wetting fluid.

The control unit can be an controller or an actuation device, which can control and regulate and/or alternatively, can be a programmable memory element having a fixedly programmable function. The control unit can furthermore receive and transmit information as well as carry out technical calculations. The control unit receives information on the ambient temperature, the ambient humidity, the amount of water of a wetting device for wetting the heat exchanger, a number of rotations of a ventilator of the heat exchanger and a geodetic level. The control unit can, for example, receive the information from one or more sensors by means of which the information can, for example, be measured or calculated. The control unit can, however, also receive further information, for example, from further sensors, from a control device, from a further control unit. The control unit can be configured as a part of the heat exchanger, this means it can, for example, be attached within our outside of a housing at the heat exchanger or, however, it can be arranged independent of the heat exchanger, for example within a room or a switching cabinet. The control unit can be connected to the sensors, the control device or to the further control unit in a signal conducting manner and can communicate, for example, by means of a cable or wirelessly for example via radio. Actuation is to be understood such that, for example, a mode of operation and/or the number of rotations and/or the amount of water can be changed by means of the control unit. Regulating is to be understood such that, for example, information on the ambient temperature, the ambient humidity, the amount of water, the number of rotations and the one geodetic level is detected or measured and a calculated or predefined value can be maintained in order to, for example, influence or to maintain a liquefaction temperature.

The ambient temperature can be measured by a temperature sensor. The temperature sensor can, for example, be a thermistor, a positive temperature coefficient thermistor, a silicon sensor, a ceramic positive temperature coefficient thermistor, a heat sensor or a thermal element. The temperature sensor can measure the information on the ambient temperature and transmit this to the control unit. The temperature sensor can be configured as a part of the heat exchanger. Alternatively, the temperature sensor can also, for example, be arranged at a housing of the heat exchanger or in the direct environment of the heat exchanger.

The ambient humidity can be measured with a humidity sensor. The humidity sensor can be a hygrometer, for example, an absorption hygrometer, a psychrometer or a dew point mirror hygrometer. The humidity sensor can transmit the information on the ambient humidity to the control unit. The humidity sensor can be configured as a part of the heat exchanger. Alternatively, the humidity sensor can also be arranged at a housing of the heat exchanger or in direct vicinity of the heat exchanger.

The control unit moreover receives information on an amount of water for the wetting device for wetting the heat exchanger, a number of rotations of a ventilator of the heat exchanger and/or a geodetic level. The amount of water can be measured with a water counter, for example with a through-flow meter or a counter. The counter can, for example, measure the amount of water within an arbitrary period of time and the through-flow meter can measure the amount of water per unit of time (such as for example volume flow, volume through-flow). The water counter can, for example, be arranged at the heat exchanger or at the wetting device, in particular at a supply line to the wetting device for a wetting fluid that can in particular be water. The number of rotations of the ventilator as a heat exchanger can be received by a control device which can be connected to the ventilator in a signal conducting manner and can set the ventilator. However, also the control unit can be connected to the ventilator in a signal conducting manner and can set the ventilator. The geodetic level can be measured either by means of a level sensor or the information on the geodetic level of the heat exchanger can be set at the control unit. The geodetic level can be measured with a level sensor. A level sensor can, for example, carry out a measurement of the geodetic level by means of a leveling device or by means of GPS or GNSS satellites or, however, be under-stood by means of a barometric level measurement.

The control unit calculates an amount of spray water in dependence on the information on ambient conditions, for example the ambient temperature, the ambient humidity, the amount of water, the number of rotations and the one geodetic level. An amount of the wetting fluid, for example water or fresh water can be understood as the amount of water or the amount of spray water. Moreover, the control unit can set the wetting device in such a way that the wetting device wets the heat exchanger with the calculated amount of spray water. The wetting device can comprise a nozzle, for example a fan nozzle or a hollow cone spray nozzle and a supply line and can be arranged at the heat exchanger. The wetting device can wet the heat exchanger, in particular the module, this means the transfer elements and/or the heat transfer elements, or a wetting mat which can, for example, be of card or a card-like material or a plastic with or without a coating. The wetting mat can, for example, be arranged above the heat exchanger and/or laterally at the heat exchanger and/or between a plurality of modules. The wetting device can, for example, be arranged above and/or laterally and/or between a plurality of modules and can wet. The wetting device can thus wet the heat exchanger from one or more spatial directions. Alternatively, the wetting device can also comprise one or more irrigation tubes that lie at the wetting mat and wet the wetting mat. The wetting fluid can evaporate at the wetted heat exchanger, wherein an excess of spray water can run off in an unevaporated manner. Thus, an additional cooling effect can be achieved due to the wetting device by means of evaporation cooling. Advantageously, the operation of the heat exchanger can be matched very precisely to the environmental conditions of the heat exchanger, for example by means of the calculated amount of spray water. The heat exchanger can make do with less water and the control unit enables an operation of the heat exchanger that is more economic and more energy-efficient. Also, the heat exchanger can be operated without a water circuit so that a treatment of water demanding in effort and cost can be omitted. Moreover, a formation of legionella can advantageously be avoided since only fresh water is provided at the heat exchanger.

In an embodiment of the invention the control unit receives information on a geodetic level and/or the calculated amount of spray water represents an estimated value for an amount of evaporation. The amount of spray water can be calculated in such a way that the amount of spray water by means of which the wetting device wets the heat exchanger nearly completely evaporates. As has already been mentioned a small excess in spray water can run off in a non-evaporated manner.

Advantageously, the heat exchanger can be wetted with precisely so much spray water as can be evaporated for this reason, for example, fresh water can be used and a water circuit for the wetting fluid can be omitted.

In an embodiment of the invention the control unit calculates a cost function in dependence on a parameter and to set the heat exchanger in such a way that the cost function is minimal. The parameter is configured as a water price for the wetting device and/or as an electricity price for the ventilator. A sum of one or more products, for example composed of a water price multiplied by the amount of water and/or the price of electricity multiplied by an amount of electricity, this means the amount of electricity consumed by the ventilator can be understood as the cost function. When the cost function is minimal, the amount of water can correspond to the calculated amount of spray water, or alternatively, a cost optimized amount of spray water and/or the amount of electricity can correspond to a cost optimized amount of electricity. Cost optimized is to be understood such that the costs for the operation of the heat exchanger are minimal and/or more energy efficient. Advantageously, the control unit can thus operate the heat exchanger in a particularly energy efficient manner and/or in a cost efficient manner in an operating state and/or mode of operation. The cost function and thus the cost for an operation of the heat exchanger can be minimized in dependence on the information present at the control unit.

In an embodiment of the invention the control unit sets a target number of rotations of the ventilator besides the amount of spray water. Moreover, the control unit sets the wetting device by means of a PI regulator. It is of advantage that the target number of rotations of the ventilator is a number of rotations that is specifically adapted to the ambient conditions and in particular corresponds to a number of rotations which minimizes the cost function. Thus, the heat exchanger, in particular the ventilator and the wetting device can be operated in a particularly cost optimized and/or economic and/or energy efficient mode of operation.

Furthermore, a heat exchanger comprising a control unit is suggested in accordance with the invention. The control unit in accordance with the invention can thus be a part of a heat exchanger. It is of advantage that the wetting device and the ventilator of the heat exchanger can be set by means of the control unit in dependence on the ambient conditions, for example in one or more mode of operations, this means they enable an operation of the heat exchanger in which the amount of water and/or the amount of electricity is ideal, this means minimal.

In an embodiment of the invention the heat exchanger comprises a module that includes a plurality of transfer elements and a plurality of heat exchanger fins. The heat exchanger fins are connected to the transfer elements in a heat conducting manner and form an air passage. A ventilator generates an air flow in the air passage. A wetting device is arranged at the heat exchanger and wets the heat exchanger with a wetting fluid.

The transfer element can, for example, be configured as a tube or in contrast thereto as an extruded section having a plurality of passages. The heat exchanger fins can be ribs or sheet metal strips that are edged. The module, this means the heat transfer elements and/or the heat exchanger fins can be made of a material that has good heat conducting properties, for example, aluminum or copper or stainless steel.

The heat exchanger can be a finned heat exchanger. The finned heat exchanger in the simplest form can comprise a tube which has a transfer element and which conducts a fluid therethrough and further comprises a plurality of fins as heat exchanger fins. The heat exchanger fins can be connected to the tube and during operation can be in connection with an exchange. This manner of construction is particularly expedient when the exchange fluid is gaseous and for example, is composed of environmental air, since this has a comparatively low heat transfer coefficient that can be compensated by a correspondingly large surface of the fins. Naturally, the finned heat exchanger can also include a plurality of tubes for more than one fluid or the tubes can be connected as required in parallel or in series. The fins or tubes can be composed of a material which is a good heat conductor, for example aluminum or copper or stainless steel. The fluid can be liquid or gaseous and can be a heat transfer medium, for example a coolant. The exchange fluid can be liquid or gaseous, for example air.

The manufacture of the finned heat exchanger can take place in accordance with a standardized process. The fins can, for example, be stamped with a press in a special tool and can be placed together in packages. The tubes can be pushed into the fins and can either be mechanically or hydraulically widened so that a very good contact and a good heat transfer can arise between the tube and the fins. The individual tubes can, for example, be connected to one another by arcs and/or a collector and distributor tube.

However, the heat exchanger can also be a plate heat exchanger or a micro-channel heat exchanger. The transfer element of the micro-channel heat exchanger can, for example, be configured as an extruded section that is manufactured from a material having good heat conductivity such as, for example, aluminum. The transfer elements can include a plurality of passages having a diameter of, for example 0.5 to 3 mm, for the heat transfer medium. The heat exchanger fins can, for example, be edged sheet metal strips in finned shape. The sheet metal strips, for example aluminum sheet metal strips, can be arranged between two extruded sections lying close to one another, so that by means of an alternating stringing together of sheet metal strips and extruded sections a module arises. This package can then be completely brazed in a brazing oven.

The heat exchanger fins are connected to the transfer elements in a heat conducting manner and form an air passage. A ventilator generates an air flow in the air passage. The heat exchanger can comprise one or more ventilators. The air flow can take place through the heat exchanger, in particular through the module.

Advantageously, the ventilator can be operated with a variable number of rotations, in particular with a target number of rotations that can be set by means of the control unit.

Moreover, a wetting device for the heat exchanger can be provided. The wetting device can comprise a nozzle, for example, a fan nozzle or a hollow truncated cone nozzle, and a supply and can be arranged at the heat exchanger. The wetting device can wet the heat exchanger, in particular the module, this means the transfer elements and/or the heat transfer elements. For this purpose, the wetting device can, for example, be arranged above and/or laterally of and/or between a plurality of modules and wet these. The wetting device can thus wet the heat exchanger from one or more spatial directions. In this connection the fluid which, for example, flows through the transfer elements and which dissipates a heat to be dissipated by the heat exchanger fins partly as sensible heat and partly as latent heat to the air flow. The dissipation of the latent heat can, for example, take place by means of the wetting fluid. For this purpose, the wetting fluid can form a liquid film forming drops at the heat exchanger, in particular at the module, this means the heat transfer element and/or the heat exchanger fins or at a wetting mat. The wetting mat can, for example, be arranged above the heat exchanger and/or laterally at the heat exchanger and/or between a plurality of modules. The wetting device can, for example, be arranged above and/or laterally of and/or between a plurality of modules and wet these. The wetting device can thus wet the heat exchanger from one or more spatial directions. Advantageously, the control unit can set the wetting device in such a way that the wetting device wets the heat exchanger with a calculated amount of spray water. The amount of spray water can thus be matched very precisely to the ambient conditions of the heat exchanger and/or the heat exchanger requires less wetting fluid in the operating state, this means it is more economic and more energy efficient.

In an embodiment of the invention, a control device associated with the ventilator receives a target number of rotations from the actuating unit and the control device sets the ventilator to a target number of rotations. Also, the wetting device is capable of wetting the module, the transfer elements and/or the heat exchanger fins and/or a wetting mat with a liquid.

Either the control unit can set the ventilator or the control device receives the target number of rotations from the control unit. In the second case, the control device can set the ventilator, this means control and regulate this. A control device can thus be understood as a device for controlling and regulating the ventilator. Thus, the heat exchanger already having a present ventilator and control device can advantageously be retrofitted with a control unit.

The wetting device can wet the module, this means the transfer element and/or the heat exchanger fins or alternatively, can also wet one or more wetting mats which can be arranged at the heat exchanger. Advantageously, the most diverse embodiments can be formed; without a wetting mat the spray water can directly evaporate, whereas with a wetting mat the spray water can, for example, be stored at the heat exchanger.

A method of regulating a heat exchanger is further suggested in accordance with the invention, wherein an amount of spray water is calculated in dependence on an ambient temperature, an ambient humidity, an amount of water of a wetting device for wetting the heat exchanger, a number of rotations of a ventilator of a heat exchanger and/or a geodetic level. The wetting device is set in such a way that the heat exchanger is wetted with the calculated amount of spray water.

The method provides the calculation of an amount of spray water in dependence on ambient conditions, for example, the ambient temperature, the ambient humidity, the amount of water, the number of rotations and the one geodetic level. The amount of water and the amount of spray water can be a wetting fluid, for example water, in particular fresh water. The wetting device can be set in such a way that the heat exchanger is wetted with the calculated amount of spray water. A wetting of the heat exchanger can be understood such that the wetting device wets a transfer element and/or a heat exchanger rib and/or a wetting mat with the fluid. Advantageously, the amount of spray water can thus be matched very precisely to the ambient conditions of the heat exchanger and the heat exchanger requires less water in the operating state and is thus more economic and/or more energy efficient. Also the heat exchanger can be operated without a water circuit, so that a water treatment demanding in effort and cost can be omitted.

The method can be carried out with the described control unit and/or the described heat exchanger.

In an embodiment of the invention the ventilator is set with a maximum target number of rotations and the wetting device is set with a maximum amount of spray water in a first mode of operation. A mode of operation can be derived by a liquefaction temperature. A liquefaction temperature in this respect can be understood as an exit temperature of the fluid, for example, for heat exchangers or for condensers. The liquefaction temperature can be dependent on the ambient temperature. Moreover, a target number of rotations of the ventilator and the amount of spray water can be set at an control unit in dependence on a target liquefaction value. A target liquefaction value can in this respect be understood as a minimum liquefaction temperature.

The target liquefaction value cannot be achieved in a first mode of operation due to a high ambient temperature and the heat exchanger can be operated at a maximum load mode of operation. In this respect, the ventilator can be set at a maximum target number of rotations and the wetting device can be set at a maximum amount of spray water. The liquefaction temperature can follow the ambient temperature in the first mode of operation.

In an embodiment of the invention the amount of spray water is calculated in such a way that this represents an estimated value for an amount of evaporation in a second mode of operation. The second mode of operation can be described as a partial load mode of operation without an efficiency mode. In this respect the ventilators can be present in a regulated mode of operation, this means the target number of rotations can be set to an arbitrary target number of rotations. Moreover, the liquefaction target value can be achieved.

If the set minimum liquefaction temperature is achieved, then the target number of rotations of the ventilator can be set, for example, to a lower number of rotations than the maximum number of rotations in order to avoid a further lowering of the liquefaction temperature. Additionally, the wetting device can be set in such a way that the heat exchanger is wetted with the calculated amount of spray water, whereby the liquefaction temperature is reduced and a performance of the heat exchanger is increased through a cooling resulting therefrom. The amount of spray water is calculated in such a way that this represents an estimated value for an amount of evaporation in a second mode of operation. For this purpose the control unit can calculate the amount of spray water by means of the ambient conditions, this means, for example, by means of the ambient humidity, the number of rotations, the amount of water and the ambient temperature in such a way that the amount of spray water is evaporated as completely as possible. Advantageously, the heat exchanger can thus be operated more energy efficiently and more economically. Moreover, a water circuit and a water treatment demanding in effort and cost can thus be omitted.

In an embodiment of the invention, in a third mode of operation, a cost function is calculated in dependence on a parameter and the heat exchanger is set in such a way that this cost function is minimal. The third mode of operation can be described as a part load mode of operation having an efficiency mode. In this respect, the ventilators can be present in a regulated mode of operation, this means that the target number of rotations can be set to a lower number of rotations than the maximum number of rotations. Moreover, the target liquefaction value can be achieved.

In the third mode of operation the amount of spray water and the target number of rotations are set in such a way that the cost function is calculated in dependence on a parameter and the heat exchanger is set in such a way that the cost function is minimal. The parameters can be configured as a price of water and/or as a price of electricity. The minimum cost function can thus be calculated with reference to predefined costs of water and costs of electricity and a cost efficient point of operation of the heat exchanger can be set. Thereby, the heat exchanger can be operated in a very energy efficient mode, since costs of water and electricity costs are minimal.

In an embodiment of the invention the amount of spray water is calculated in dependence on the geodetic level and/or a mode of operation of the heat exchanger is derived in dependence on a liquefaction temperature. By means of the control unit it can be calculated with reference to the ambient conditions which mode of operation is ideal, this means whether it is, for example, more cost-effective to dissipate heat by evaporation based on cooling or by convection. In dependence on whether the liquefaction target value is achieved the regulator is present either in the full load mode of operation and/or in a part load mode of operation. The mode of efficiency can be activated in the control unit.

A large advantage of the control unit in accordance with the invention, of the heat exchanger in accordance with the invention and of the method in accordance with the invention is the setting of the different mode of operations. Thereby, at any point in time an operation ideally matched to the ambient conditions is enabled and the compensation of jumps in performance is enabled. In contrast to the prior art the regulation of the heat exchanger can thus be improved totally, since it is set with a higher precision.

Further advantageous measures and modes of carrying out the method result from the dependent claims.

Further advantages result from the following description of the Figures. In the Figures an embodiment of the invention is illustrated. The Figures, the description of the Figures and the claims include numerous features in combination with one another. The person of ordinary skill in the art will expediently also consider these features individually and combine these to suitable further combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail hereinafter with reference to the drawings.

FIG. 1 is a schematic illustration of a first embodiment of a heat exchanger having an control unit;

FIG. 2 is a schematic illustration of a second embodiment of a heat exchanger having a wetting device and an control unit;

FIG. 3 is a schematic representation of a time versus temperature diagram for an explanation of the method; and

FIG. 4 is a schematic representation of a third embodiment of a heat exchanger with a wetting device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a schematic representation of a first embodiment of a heat exchanger 2 having a control unit. The heat exchanger 2 comprises a module 5 and a ventilator 4. The module 5 in turn includes a plurality of transfer elements and a plurality of heat exchanger fins which are connected to the transfer elements in a heat conducting manner and form an air passage. The ventilator 4 generates an air flow in the air passage. Moreover, a wetting device (3, see FIG. 2) is arranged at the heat exchanger 2, said wetting device wetting the heat exchanger 2 with a wetting fluid.

Furthermore, a control unit 1 is provided at the heat exchanger 2. The control unit 1 receives information on an ambient parameter, in particular on

-   -   an ambient temperature,     -   an ambient humidity,     -   an amount of water of a wetting device 3 for wetting the heat         exchanger 2,     -   a number of rotations 41 of a ventilator 4 of the heat exchanger         2 and/or a geodetic level.

The ambient temperature can be measured by means of a temperature sensor 8 and the information on the ambient temperature can be received by the control unit 1. Likewise the ambient humidity can be measured by a humidity sensor 7 and the information on the ambient humidity can be received by the control unit 1. The amount of water of the wetting device 3 is measured with a water counter 11, for example by a through-flow meter or a counter. The number of rotations 41 of the ventilator 4 are received by the control unit 1 which is connected to the ventilator 4 in a signal conducting manner. The geodetic level is measured by a level sensor 9 and the information on the geodetic level is received by the control unit 1. The control unit 1 calculates an amount of spray water 31 in dependence on the said information and sets the wetting device 3 in such a way that the wetting device 3 wets the heat exchanger 2 with the calculated amount of spray water 31.

In FIG. 2 a schematic illustration of a second embodiment of a heat exchanger 2 having a wetting device 3 and a control unit 1 is shown. The FIG. 2 substantially corresponds to the FIG. 1 which is why reference is only made to the differences. In this respect, a control device 6 is provided which sets the ventilator 4. The control unit 1 is connected to the control device 6 in a signal conducting manner. The control unit 1 receives the number of rotations 41 from the control device 6 and the control device receives a target number of rotations from the control unit 1. As has already been mentioned, the control device 6 and the control unit 1 can also be configured as one piece, this means that the control device 6 can be configured as a part of the control unit 1.

The wetting device 3 is arranged in such a way that the modules 5 are wetted from the interior of the heat exchanger 2, for example by spray nozzles. Also the heat exchanger is operated without a water circuit such that a water treatment demanding in effort and cost can be omitted.

FIG. 3 shows a schematic illustration of a time versus temperature diagram for the explanation of the method. At the abscissa a number of operating hours per year n[h/a] is shown and the temperature T in degrees C. is applied on the ordinate. The three paths of the function show the accumulated ambient temperature and liquefaction temperature in dependence on the number of hours. The path of the function 95 corresponds to the path of the accumulated ambient temperature, the path of the function 94 corresponds to the path of the accumulated liquefaction temperature with the wetting device 3 and the path of the function 93 corresponds to the accumulated liquefaction temperature without the wetting device 3. The vertical lines 90, 91 bound different modes of operation. The dotted vertical line 90 is the boundary between a full load mode of operation (region 2) and a part load mode of operation for a dry operating manner (the region to the right of the dotted vertical line 90). The continuous vertical line 91 bounds the full load mode of operation (region 1) from the part load mode of operation (region 2) when the wetting is additionally active. The dotted horizontal line 92 corresponds to the liquefaction target value.

The target number of rotations of the ventilators 4 set at the control unit 1 is set in dependence on the liquefaction target value. If this liquefaction target value is not achieved due to high ambient temperatures then the ventilators 4 work at a full number of rotations 41 and the heat exchanger 2 is present in the full load mode of operation. In this operating state the liquefaction temperature follows the ambient temperature. If the set liquefaction target value is achieved then the number of rotations 41 of the ventilators is down-regulated in order to avoid a further reduction of the liquefaction temperature. In the second or third mode of operation, the liquefaction temperature is reduced by the additional wetting of the heat exchanger 2, whereby the boundary between the full load mode of operation (region in the diagram characterized with 1) and the part load mode of operation (region characterized with 2 in the diagram) is displaced.

FIG. 4 is a schematic illustration of a third embodiment of a heat exchanger 2 having a wetting device 3 and a PI regulator 10. FIG. 4 substantially corresponds to FIG. 1 which is why reference is only made to the differences. In this respect, the control unit (not illustrated) sets the wetting device 3 by means of the PI regulator 10. The PI regulator 10 sets a regulating ball valve 12 which sets an inflow of the wetting fluid to the wetting device 3. The wetting device 3 is configured as a pearl hose which lies on one or more wetting mats (not illustrated). A water counter 11 measures the amount of water of the fluid which flows towards the wetting device 3. An outlet valve 13 is additionally provided which empties the wetting device 3 if required. A scheme of regulation can be configured in such a way that an amount of water or an amount of spray water 31 set by the PI regulator 10 flows towards the wetting device 3. In this connection, the water counter 11 detects the amount of water and the PI regulator 10 sets the amount of water to the calculated amount of spray water 31 with reference to a deviation in regulation. 

1. A control unit for a heat exchanger, the control unit being programmed to receive information on an ambient temperature, an ambient humidity, an amount of water of a wetting device for wetting the heat exchanger and a number of rotations of a ventilator of the heat exchanger and to calculate an amount of spray water based on the information and set the wetting device to wet the heat exchanger with the calculated amount of spray water.
 2. The control unit in accordance with claim 1, wherein the control unit is programmed to receive information on at least one of a geodetic level and the calculated amount of spray water, representing an estimated value for an amount of evaporation.
 3. The control unit in accordance with claim 1, wherein the control unit is programmed to to calculate a cost function based on a parameter and to set the heat exchanger to minimize the cost function.
 4. The control unit in accordance with claim 3, wherein the parameter is at least one of a water price for the wetting device and an electricity price for the ventilator.
 5. The control unit in accordance with claim 1, wherein the control unit is programmed to set a target number of rotations of the ventilator.
 6. The control unit in accordance with claim 1, wherein the control unit is programmed to set the wetting device with a PI regulator.
 7. A heat exchanger comprising the control unit in accordance with claim
 1. 8. The heat exchanger in accordance with claim 7, comprising a module including a plurality of transfer elements and a plurality of heat exchanger fins connected to the transfer elements in a heat conducting manner and forming an air passage, and a ventilator configured to generate an air flow in the air passage, the wetting device being arranged at the heat exchanger and configured to wet the heat exchanger with a wetting fluid.
 9. The heat exchanger in accordance with claim 7, further comprising a control device associated with the ventilator, configured to receive a target number of rotations from the control unit, and configured to set the target number of rotations at the ventilator.
 10. The heat exchanger in accordance with claim 7, wherein the wetting device is configured to wet at least one of the module, the transfer elements, the heat exchanger fins and a wetting mat with liquid.
 11. A method of regulating a heat exchanger, comprising: calculating, with a control unit, an amount of spray water based on an ambient temperature, an ambient humidity, an amount of water of a wetting device for wetting the heat exchanger and a number of rotations of a ventilator of the heat exchanger; and setting, with a control unit, the wetting device such that the heat exchanger is wetted with the calculated amount of spray water.
 12. The method in accordance with claim 11, further comprising, in a first mode of operation, setting the ventilator to a maximum target number of rotations, and setting the wetting device to a maximum amount of spray water.
 13. The method in accordance with claim 12, wherein, in a second mode of operation, the calculating the amount of spray water includes calculating an estimated value for an amount of evaporation.
 14. The method in accordance with claim 11, further comprising, in a third mode of operation, calculating a cost function based on a parameter and setting the heat exchanger to minimize the cost function.
 15. The method in accordance with claim 11, wherein calculating the amount of spray water based on at least one of a geodetic level and a mode of operation of the heat exchanger is derived in dependence on a liquefaction temperature. 